The demand for alternative non-meat protein sources in the 1950s led to the development of a number of processes for texturing plant proteins or mixtures of plant and animal proteins to form meat-like materials.
These processes are very diverse, but in many cases three common steps are involved, vizg (1) an initial hydration and mixing step to form a slurry or dough, followed by (2) a shearing (and in some cases heating) step to denature proteins and produce aligned protein fibres (a reducing agent is often present at this stage to promote denaturation by rupture of disulphide bonds), and finally (3) a setting step to fix the fibrous structure, setting often being achieved by rapid temperature and/or pressure change, rapid dehydration or chemical fixation. The restructured material is usually extruded through a die orifice to shape the product prior to setting. One of the most common methods of producing textured proteins is by extrusion cooking (see Gutcho, M. (1973), "Textured foods and allied products", Food Technology Review No. 1, Noyes Data Corporations Park Ridge, N.J., USA, and Harperg J. M. (1981), Chapter 13 "Textured Plant Proteins", in Extrusion of Foods Vol. II, CRC Press Inc., Boca Raton, Fla., the contents of which are incorporated herein by reference).
In this process a protein-rich flour (typically 50-80% protein) is fed into a closed barrel containing one or two screw shafts. The screws convey the material forwards where it is mixed with water and kneaded to form a dough. The dough is then conveyed forward into a zone containing screw elements designed to impart shear, this area also being hot (100-170 degrees centigrade) and under pressure (100-1000 psi). These extreme conditions cause the material to melt and adopt a fibrous character. The fibres become aligned in the direction of shear applied by the screw elements.
The melt is then forced through a single, or a number, of die orifices. As the material extrudes through the die, super-heated water present in the melt flashes off as steam, causing a simultaneous expansion ("puffing") of the material. At this point the material sets, and the process therefore produces a continuous stream of textured product. This process is shown schematically in FIG. 7.
Although fairly dry at this stages the product is usually dried further to increase shelf-life. Before use the product is fully rehydrated (the water absorption of such products is usually in the region of three times their own weight).
Natural fibrous protein sources, such as meat and mycoprotein (sold under the Trade Mark Quorn), have textures which elicit distinctive sensations during chewing and breakdown in the mouth. This mouthfeel is an extremely important acceptability/quality parameter of meat and meat-substitutes, and there is a window of texture associated by consumers with various protein-based products. For example, the rate at which the product breaks down on chewing, the number of chews required before the material can be swallowed, the textures exposed to the teeth and tongue during chewing are all important in determining the acceptability of the product, especially in the case where the product is a meat substitute.
Extrusion of conventional textured protein products, such as those made with soya or wheat proteins tend to result in very fibrous material with a meat-like appearance. However, when hydrated, the system of fibres form a resilient and continuous matrix. The result is a very elastic and tough product which exhibits a poor mouthfeel. Many products have rubbery, tough, slimy and spongy mouthfeels.
One solution to this problem is to use the textured protein products as meat substitutes or analogues in comminuted form. However, this limits their application to products where minced meat would conventionally be used, for example in burgers, sausages and similar products.
Another solution has been to dilute the protein with starchy materials, such as wheat flour or corn starch. However, although this approach has been found to soften the products it does not impart a meat-like mouthfeel--the product is often still too chewy and sliminess may be increased.
It is an object of the present invention to provide food products (for example, textured food products) having an improved mouthfeel.